Umbrella base



FIG. 1 is a top perspective view of an umbrella base showing our new design;

FIG. 2 is a left side elevational view thereof, the right side and front and rear being a mirror image; and,

FIG. 3 is a top plan view thereof.

The circle shown in broken lines in FIGS. 3 represents the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purpose only. None of the broken lines form a part of the claimed design. The bottom of the umbrella is unornamented and forms no part of the claimed design 

CLAIM The ornamental design for an umbrella base, as shown and described. 